Isolation of the pellicle of Toxoplasma gondii (Protozoa, Coccidia): characterization by electron microscopy and protein composition.

Two methods were compared for the isolation of the Toxoplasma gondii pellicle: centrifugation using a discontinuous sucrose gradient and affinity purification by microspheres activated with protein A. Electron microscopy showed that these two means of purification gave similar results, although better yields were obtained with the former than with the latter. Proteins of membrane fractions isolated using sucrose gradient were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Bands in the molecular-weight regions of 19, 22, 35, and 79 kDa appeared to be associated with the T. gondii pellicle.